Shuttle commander Eileen Collins walks to training aircraft
Terry Renna  /  AP
Space shuttle commander Eileen Collins, left, waves as she walks to a training aircraft with support crew members early Friday at Kennedy Space Center. While engineers work on the shuttle's sensor problem, Discovery's crew continues to prepare for the mission.
msnbc.com staff and news service reports
updated 7/15/2005 6:14:36 PM ET 2005-07-15T22:14:36

The first space shuttle launch since the Columbia tragedy will have to wait at least a few days more. NASA decided Friday to take the shuttle off launch status, allowing personnel not involved in troubleshooting to go home for the weekend.

No new launch date was announced. Deputy shuttle program manager Wayne Hale said the agency was "going forward on a day by day basis." The earliest possible time might be the end of next week, Hale said, but it would require a "lucky find."

Space shuttle Discovery had been due to blast off Wednesday, but one of the fuel tank's four hydrogen sensors failed a routine test as the clock ticked down toward liftoff and NASA was forced to call off the launch. Engineers have been working to figure out why ever since, and early Friday, workers drained toxic propellants from the onboard power generators to allow them safe access to more areas.

While some members of the launch team were released, Hale made it clear that the troubleshooting effort was going on throughout the weekend. "The entire resources of the agency are behind us," he said. "We're here for the duration."

Seven people not going home are Discovery's crew members. For now, the astronauts are staying at Kennedy Space Center, Hale said.

The current launch opportunity extends until July 31. After that, the next liftoff window begins Sept. 9 — the timing is determined by the space station's orbital position as well as NASA's desire to launch at least the first two shuttle missions during daylight hours.

Hale indicated a July launch was still possible and said that the shuttle would be able to launch four days after any fix is made.

Discovery's mission will mark NASA's return to flight after more than two years of investigations, upgrades and reforms in the wake of the shuttle Columbia's catastrophic breakup in February 2003, in which all aboard were killed. The flight's main aims are to resupply the international space station — and more importantly, demonstrate all the safety measures that NASA has instituted since Columbia's loss.

Because of Columbia, NASA has focused intently on fully resolving any issues of concern. Those issues range from the shedding of foam insulation from the shuttle's external fuel tank, which was implicated in the Columbia accident, to the current unresolved glitch.

'Unexplained anomaly'
NASA has hundreds of engineers around the country trying to figure out the "unexplained anomaly" in the fuel-tank sensor, Hale said Thursday.

The glitch involves a low-level sensor in the liquid-hydrogen compartment of Discovery's external fuel tank. During a routine test in the final hours of Wednesday's countdown, the launch team commanded the sensors to show an empty, or "dry," reading. Three of the sensors did just that, passing the test. But one flunked, continuing to show a "wet" reading.

Unfortunately, all four sensors have to pass the test, and so managers stopped the countdown and brought Discovery's crew back out of the shuttle orbiter.

On Wednesday night, the fuel tank was drained of its liquid hydrogen and liquid oxygen, and the sensors were checked again. For about three hours afterward, the troublesome sensor continued to indicate there was hydrogen left in the tank, Hale said. But then it began showing correctly that the tank was dry, he said.

"Right now, the sensor indication is as it should be," he said, "which represents something of a problem for our troubleshooting team."

The mission management team is drawing up a full-scale troubleshooting plan, which involves poring over the test data as well as the documentation for past tests and the origins of the sensor system components. The problem could lie in the sensor itself, or in the electronic circuits that interpret sensor readings, or in the connective wiring.

Under some scenarios, Discovery might have to be rolled off the launch pad and into NASA's 52-story-high Vehicle Assembly Building, Hale said. That could cause the shuttle to miss the July launch opportunity altogether.

MSNBC's Alan Boyle, NBC's Jay Barbree and Reuters contributed to this report.

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